The present invention relates to metal halide light bulbs. More particularly, it refers to a strobe light caused by a high intensity discharge metal halide lightbulb utilizing switching circuitry.
While metal halide lamps offer far greater lumens per watt than tungsten halogen lamps, bulb lifetimes are frequently shortened as applications require rapid start up and hot re-strike characteristics in higher wattage lamps. Typical prior art metal halide light bulbs are described in U.S. Pat. No. 3,259,777, wherein an iodide gas is produced by a salt of iodide such as indium triiodide. Once this type of lamp""s arc discharge is disrupted, the lamp cannot be restarted without significant delay of up to one minute. U.S. Pat. No. 3,989,970 describes an improvement utilizing metal fins at the external terminals to cool the electrodes and enhance more rapid start up after arc discharge is disrupted.
In U.S. Pat. No. 3,780,342, a circuit is described for starting a high operating temperature lamp. An initial starting pulse of 8000 volts creates an arc between the electrodes. The circuit reduces the voltage to 40 volts whereupon the circuit performs a ballasting function to regulate the operating circuit. This type lamp also has a slow restart time after interruption of current in the power supply.
U.S. Pat. No. 4,779,026 describes a metal halide high discharge lamp with at least one electrode shaped to have a narrow V form with the apex of the V facing the other electrode of the lamp. This configuration provides a light output at an improved speed.
U.S. Pat. No. 5,270,608 describes a metal halide high intensity discharge lamp reducing sodium migration from an arc tube by inclusion of a shroud supported by a mechanical mounting structure.
U.S. Pat. No. 5,291,100 describes a low DC input, low wattage high intensity discharge metal halide lamp having a regulated power supply. The lamp is controlled by a switching and voltage regulation circuit with an adjustable duty cycle oscillator and driver feeding a main ballast transformer.
U.S. Pat. No. 5,604,406 describes a lamp assembly including a circuit board for creating a rapid start metal halide bulb.
None of the above high intensity discharge metal halide lamps can be used as a strobe because of a lag between stop and start up. A high intensity discharge metal halide used as a strobe would have distinct advantages over standard strobe lights currently in use, since a metal halide bulb has a longer life than a filament or halogen light bulb. Moreover, high intensity discharge metal halide bulbs produce more light power output than filament or halogen light bulbs. A need exists for a flashing high intensity discharge metal halide lamp.
This invention describes a high intensity discharge metal halide lamp that has a circuit and structure allowing for flashing similar to currently used strobe lights but with a longer life advantage and more light power output characteristic of a high intensity discharge metal halide lamp.
The lamp employed contains a quartz or fused silicon arc tube surrounding a gas tight envelope containing mercury, a metal halide, a rare earth gas and a pair of end to end spaced apart tungsten electrodes. The electrodes are attached at their distal ends to a molybdenum foil. The arc tube is hermetically sealed within a borosilicate glass envelope. The lamp receives from an electrical circuit an initial charge of at least 30,000 volts to cause ignition. Thereafter, the electrical circuit is maintained with 100-2000 watts as the circuit is automatically broken and connected continuously with a timer in the circuit. A single driver actuates multiple lamps.